1. Technical Field
The present invention relates to integrated circuits, and more particularly to active matrix circuits and fabrication processes having hybrid devices and bipolar transistors integrated therein.
2. Description of the Related Art
In applications such as active-matrix displays, control/driving circuitry is implemented with standard very large scale integration (VLSI) devices and connected to a back-plane (an array of thin film transistors (TFTs) used for driving passive elements such as organic light emitting diodes (OLEDs) and liquid crystal displays (LCDs)) externally. The TFTs are typically comprised of a-Si:H or metal-oxide semiconductors because of their low-cost, large-area compatibility and low deposition temperatures, which are compatible with low-cost substrates. However, the poor mobility and stability of these devices is not sufficient for very high-resolution and low-power displays, such as, e.g., pico-projectors and micro-displays. The limited performance of these conventional devices (particularly with respect to mobility and therefore drive current and switching speed) is limited by the non-crystalline nature of the semiconductor materials.
Crystalline semiconductors result in high processing temperatures and are not compatible with low-cost substrates used with amorphous and polycrystalline devices. Non-monolithic integration of the driver/control circuitry also limits the compactness and lightness of the display, which are important considerations for mobile applications.
Applications such as active matrix displays need high performance scanning, control and hold circuits, which typically implemented by complementary metal oxide semiconductor (CMOS) technology and are integrated off-chip. The backplane section (transistors and pixels) are typically comprised of lower-performance devices, e.g., a-Si:H on glass. Higher performance devices are desired for higher resolution/lower power.